Investigation of the ground thermal potential in tunisia focused towards heating and cooling applications H. Ben Jmaa Derbel a,b, * , O. Kanoun c a Research Unit on Renewable energies and ELEctric Vehicles (RELEV), Ecole Nationale d’Ingénieurs de Sfax, B.P. 1173, 3038 Sfax, Tunisia b Faculté des Sciences de Sfax, B.P. 802, 3018 Sfax, Tunisia c University of Chemnitz, Germany article info Article history: Received 6 June 2008 Accepted 19 January 2010 Available online 22 January 2010 Keywords: Thermal modelling Earth pipe system Soil temperature model Energy abstract In this paper, an experiment has been conducted in order to record the ground temperature at different depths during 2006 in a suburb of Sfax (Tunisia) which represents an example of the South-Mediterra- nean climate. The temperature of the soil has also been calculated using a thermal model taking into account properties of the soil and meteorological conditions. Experimental results are compared with theoretical predictions. In order to estimate the influence of the soil properties on the ground tempera- ture, different soil thermal conductivities are tested. A simplified model of an earth pipe system is devel- oped. The cooling and heating capabilities produced by such a system are evaluated. This model is validated against an other published experimental model. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Heating and air conditioning systems are currently regarded as one of the most energy consuming devices. When the temperature of the ambient air rises during summer and decreases during win- ter to an undesirable level, it is of primary importance to consider an energy source for improving comfort which is achieved when the indoor temperature is between 22 and 27 °C. The vast storage of thermal energy of the earth has focused re- search and development projects towards the use of ground as a heat source considering buried pipe systems. In buried pipe sys- tems, the nearly constant and stored thermal energy of earth at a certain depth is usually extracted by means of an earth fluid heat exchanger. By allowing the fluid to flow in buried pipes, there oc- curs an energy exchange between the fluid flowing through the ex- changer and the underground soil depending on the difference of their temperatures. This exchange of thermal energy induces vari- ations in the temperature of the moving fluid and the soil around the pipe. In summer, the warm fluid provides its heat content to the bur- ied pipe by convection, which is then dissipated to the earth by conduction. The cool fluid from the heat exchanger flows into the building spaces to create required thermal conditions. In winter, when cold fluid flows through the buried pipes, there occurs a transfer of heat from the surrounding earth to the pipes by conduction and then to the fluid by convection yielding the in- crease of the delivery fluid temperature. When coming up, the fluid provides its heat to the building spaces. From an academic point of view, many works regarding the use of the soil temperature have been reported in the literature. In North Carolina USA, Dhaliwal and Goswami [1] presented a theo- retical model of an earth cooling pipe system. They found a good agreement when they compared theoretical results with experi- mental data. In Japan, Zhang et al. [2] conducted experimental studies using an earth cooling pipe, which yields a reduction in the indoor temperature of a test house Kumamoto by more than 1 °C. A similar study was carried out by Thanu et al. [3] in the Gur- gaon, about 45 km South-West of New Delhi in India. They found out that a high effectiveness of such system can be gained during summer months. Furthermore, it has been clearly shown that the variations in the temperature, relative humidity and humidity ratio of the fluid (air) are damped as it passes through the system. Sodha et al. [4] built two cooling systems including a large earth-air tun- nel system in two different regions in India. The effectiveness of both systems in preconditioning ambient air during the summer has been proven. They found that the daily average cooling capa- bility could reach about 512 kWh and that its heating capability could reach about 270 kWh. In Greece, Mihalakakou et al. [5] mod- elled the thermal performance of earth to an air heat exchanger. They developed a new numerical model which describes the simultaneous heat and mass transfer inside the tube. A good 1359-4311/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2010.01.022 * Corresponding author. Address: Research Unit on Renewable Energies and ELEctric Vehicles (RELEV), Ecole Nationale d’Ingénieurs de Sfax, Tunisia. E-mail address: h.derbel@fss.rnu.tn (H. Ben Jmaa Derbel). Applied Thermal Engineering 30 (2010) 1091–1100 Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng